Recently, as components of semiconductor units, electronic devices having various types of electronic components mounted on circuit members of circuit substrates are being used, in which the electronic components include a semiconductor device, a dye sublimation thermal printhead device and a thermal ink-jet printhead device, wherein the semiconductor device includes an insulated gate bipolar transistor (IGBT) device, an intelligent power module (IPM) device, a metal oxide semiconductor field effect transistor (MOSFET) device, a light emitting diode (LED) device, a freewheeling diode (FWD) device, a giant transistor (GTR) device, and a Peltier device.
A circuit substrate with a circuit member mounted electronic components is a circuit substrate, in which a circuit member and a heat radiation member made of a metal having high thermal conductivity are respectively bonded through a brazing material to each of principal surfaces on both sides of the support substrate made of insulating ceramics. As for a support substrate made of insulating ceramics, a silicon nitride substrate having excellent thermal conductivity and mechanical properties is attracting attention.
As an example of such a silicon nitride substrate, Patent Document 1 proposes a silicon nitride substrate for mounting a circuit substantially made of a silicon nitride sintered body substrate made of silicon nitride particles and a grain boundaries, wherein the surface of the substrate has the following properties: the area ratio of the silicon nitride grains is 70 to 100% when the total area ratio of the silicon nitride grains and the grain boundaries on the surface of the sintered body substrate is 100%; the distance (L) between the highest peak of the silicon nitride grains exposed on the surface and the lowest bottom of the silicon nitride grains or the grain boundaries is 1.5 to 15 μm; and the surface has centerline average surface roughness (Ra) of 0.2 to 5 μm.
As methods for conditioning the surface texture of the silicon nitride substrate, Patent Document 1 discloses methods for mechanically removing the grain boundaries by mechanical processing such as sand blasting, shot blasting, grit blasting or hydroblasting.